The proposed research will concentrate on studies of hepatitis B virus (HBV) and hepatitis B antigen (HBAg). Serum or other specimens will be obtained from antigenemic patients with acute, persistent or chronic active hepatitis B. The HBAg's will be examined by electron microscopy to determine the proportion of 42 nm spheres (Dane particles), tubules, and 20 nm spheres. The different morphological forms of HBAg will be concentrated and purified, partially or completely. The concentrated or purified preparations will be analyzed for their peptide composition, antigenicity with respect to subtype determinants, and infectivity for tissue cultures or nonhuman primates; and antibody response to HBV or HBAg and the capacity of antibodies to neutralize HBV will be estimated. The data obtained will be correlated with clinical parameters such as severity of disease and their diagnostic or prognostic significance will be evaluated.